The Janus kinases (JAK) are a family of tyrosine kinases consisting of JAK1, JAK2, JAK3 and TYK2. The JAKs play a critical role in cytokine signaling. The down-stream substrates of the JAK family of kinases include the signal transducer and activator of transcription (STAT) proteins. JAK/STAT signaling has been implicated in the mediation of many abnormal immune responses such as allergies, asthma, autoimmune diseases such as transplant rejection, rheumatoid arthritis, amyotrophic lateral sclerosis and multiple sclerosis as well as in solid and hematologic malignancies such as leukemias and lymphomas. JAK2 has also been implicated in myeloproliferative disorders, which include polycythemia vera, essential thrombocythemia, chronic idiopathic myelofibrosis, myeloid metaplasia with myelofibrosis, chronic myeloid leukemia, chronic myelomonocytic leukemia, chronic eosinophilic leukemia, hypereosinophilic syndrome and systematic mast cell disease.
The Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK) family are effectors of Ras-related small GTPase Rho. The ROCK family includes p160ROCK (ROCK-1), ROKα/Rho-kinase/ROCK-II, protein kinase PKN, and citron and citron kinase. ROCK has been implicated in various diseases and disorders including hypertension, chronic obstructive pulmonary disease, cerebral vasospasm, coronary vasospasm, bronchial asthma, erectile dysfunction, glaucoma, vascular smooth muscle cell proliferation, myocardial hypertrophy, malignoma, ischemia/reperfusion-induced injury, endothelial dysfunction, Crohn's Disease and colitis, neurite outgrowth, Raynaud's Disease, angina, Alzheimer's disease, atherosclerosis, and cardiac hypertrophy and perivascular fibrosis.
Protein kinase A (PKA; also known as cAMP-dependent protein kinase) is a tetrameric holoenzyme, which contains two catalytic subunits bound to a homo-dimeric regulatory subunit (which acts to inhibit the catalytic sub-units). On binding of cAMP (enzyme activation), the catalytic subunits dissociate from the regulatory subunits to yield the active serine/threonine kinase. Three isoforms of the catalytic subunit (C-α, C-β and C-γ) have been reported to date, with the C-α subunit being the most extensively studied, primarily because of its elevated expression in primary and metastatic melanomas. PKA has been shown to regulate many vital functions including energy metabolism, gene transcription, proliferation, differentiation, reproductive function, secretion, neuronal activity, memory, contractility and motility.
Accordingly, there is a great need to develop compounds useful as inhibitors of protein kinases, including JAK family, ROCK and PKA kinases. In particular, it would be desirable to develop compounds that are useful as inhibitors of JAK2 and JAK3.